(06) Express the following as the sum of two odd primes.
(a) 44 = 3 + 41 (Both 3 and 41 are odd primes)
(b) 36 = 5 + 31 (Both 5 and 31 are odd primes)
(c) 24 = 5 + 19 (Both 5 and 19 are odd primes)
(d) 18 = 5 + 13 (Both 5 and 13 are odd primes)
(07) Give three pairs of prime numbers whose difference is 2.
Sol:
Three pairs of prime numbers whose difference is 2:
a. 5,7
b. 11,13
c. 17,19
In each case, difference between two numbers in a pair is 2.
(08) Which of the following numbers are prime?
Sol:
(a) 23 – It has only two factors; 1 and 23, therefore, 23 is a prime number.
(b) 51 – It has more than two factors; 1, 3, 17 and 51, therefore, 51 is not a prime number.
(c) 37 – It has only two factors; 1 and 37, therefore, 37 is a prime number.
(d) 26 – It has more than two factors; 1, 2, 13 and 26, therefore, 26 is not a prime number.
(09) Write seven consecutive composite numbers less than 100 so that there is no prime number between them.
Sol:
Seven consecutive numbers less than 100 so that there is no prime number between them are
90, 91, 92, 93, 94, 95 and 96.
(10) Express each of the following numbers as the sum of three odd primes:
Sol:
(a) 21 = 3 + 5 + 13
(b) 31 = 3 + 5 + 23
(c) 53 = 3 + 7 + 43
(d) 61 = 3 + 5 + 53